Recently, NGN (Next Generation Network) has become mainstream in respective carriers. In a communication system compatible with the NGN, a communication device is often required for acquiring, by use of DHCP (Dynamic Host Configuration Protocol), SIP information such as a user ID (Identifier) and an IP (Internet Protocol) address from a SIP network at the carrier side, and for automatically executing registration processing to the SIP network.
Note that as an example of such a communication system, there has been known an IP telephone system disclosed by PTL 1.